How to create multiple clones of a VM in KVM/libvirt

cloningkvm-virtualizationlibvirt

I (will) have a VM in libvirt (using QEMU/KVM) that I will set up and consider the "gold master". I would then like to be able to clone it 'n' times to create multiple systems. What is the best way to do this, and how best to "individualize" the cloned systems after they are instantiated? The hypervisor platform is:

OS: Ubuntu 12.04.2

Hypervisor pkg: qemu-kvm 1.0+noroms-0ubuntu14.8

Libvirt: 1.0.4 (compiled from source)

I am managing the VMs from another system (Fedora 18 OS) using virt-manager 0.9.5

I know I can shut down the VM and then use virt-manager's "Clone…" function, but am wondering if there is a better way (especially if I could do multiple clones at once, not sure if that's possible or not…)

Best Answer

To massively clone (baseline or even customized) installations I would say that the best method is to set up a PXE+TFTP server and provide a preseed/kickstart file.

Add your config management tool of choice (puppet/chef/cfengine/other) to the mix and you will have a powerful framework to deploy as many clones as you need. Moreover, add local mirrored repositories to increase speed.

The upper limit for simultaneously deployed clones will be the ethernet and I/O throughput you can sustain.

Related Solutions

Ubuntu – Forwarding ports to guests in libvirt / KVM

The latest stable release for libvirt for Ubuntu is version 0.7.5, which doesn't have some newer features (i.e. script hooks and network filters) which make automatic network configuration easier. That said, here's how to enable port forwarding for libvirt 0.7.5 on Ubuntu 10.04 Lucid Lynx.

These iptables rules should do the trick:

iptables -t nat -I PREROUTING -p tcp -d 1.2.3.4 --dport 80 -j DNAT --to-destination 10.0.0.1:80
iptables -t nat -I PREROUTING -p tcp -d 1.2.3.4 --dport 22 -j DNAT --to-destination 10.0.0.2:22
iptables -I FORWARD -m state -d 10.0.0.0/24 --state NEW,RELATED,ESTABLISHED -j ACCEPT

The default KVM NAT config provides a rule similar to the 3rd I gave above, but it omits the NEW state, which is essential for accepting incoming connections.

If you write a startup script to add these rules and you're not careful, libvirt 0.7.5 overrides them by inserting its own. So, in order to make sure these rules are applied properly on startup, you need to make sure libvirt has initialized before you insert your rules.

Add the following lines to /etc/rc.local, before the line exit 0:

(
# Make sure the libvirt has started and has initialized its network.
while [ `ps -e | grep -c libvirtd` -lt 1 ]; do
        sleep 1
done
sleep 10
# Set up custom iptables rules.
iptables -t nat -I PREROUTING -p tcp -d 1.2.3.4 --dport 80 -j DNAT --to-destination 10.0.0.1:80
iptables -t nat -I PREROUTING -p tcp -d 1.2.3.4 --dport 22 -j DNAT --to-destination 10.0.0.2:22
iptables -I FORWARD -m state -d 10.0.0.0/24 --state NEW,RELATED,ESTABLISHED -j ACCEPT
) &

The sleep 10 above is a hack to make sure the libvirt daemon has had a chance to initialize its iptables rules before we add our own. I can't wait until they release libvirt version 0.8.3 for Ubuntu.

Ubuntu – how to rename a VM using libvirt+KVM

run

virsh dumpxml name_of_vm > name_of_vm.xml

Undefine the old vm to prevent an error because of an duplicate UUID.

virsh undefine name-of-vm

Edit the xml file then import it.

virsh define name_of_vm.xml

Of course you will have to stop and start the vm for the changes to take effect

virsh destroy name_of_vm
virsh start name_of_vm

Best Answer

Related Solutions

Ubuntu – Forwarding ports to guests in libvirt / KVM

Ubuntu – how to rename a VM using libvirt+KVM

Related Topic